MergeSort in Oz

local A B MyMerge MySplit MyMergeSort in
   fun {MyMerge Xs Ys}
      case Xs#Ys
      of Xs#nil then
     Xs
      [] nil#Ys then
     Ys
      [] (X|Xr)#(Y|Yr) then
     if X<Y then
        X|{MyMerge Xr Ys}
     else
        Y|{MyMerge Xs Yr}
     end
      end
   end
   proc {MySplit Xs ?Ys ?Zs}
      case Xs
      of nil then
     Ys = nil
     Zs = nil
      [] [X] then
     Ys = [X]
     Zs = nil
      [] X1|X2|Xr then Yr Zr in
     Ys = X1|Yr
     Zs = X2|Zr
     {MySplit Xr Yr Zr}
      end
   end
   fun {MyMergeSort Xs}
      case Xs
      of nil then
     nil
      [] [X] then
     [X]
      [] _|_ then Ys Zs in
     {MySplit Xs Ys Zs}
     {MyMerge {MyMergeSort Ys} {MyMergeSort Zs}}
      end
   end
   A = [5 2 6 4 1]
   B = {MyMergeSort A}
   {Browse B}
end